In a communication system, signals comprising data are typically transmitted from a transmitter to a receiver via a communication medium or communication channel contained within a communication link. The transmitter modulates and transmits these signals at a specified modulation type (e.g. QPSK, 16-QAM, and 64-QAM) and at a specified data or signaling rate (e.g. 160 k bits per second) within the communication medium. Typically, the communication medium (also referred to simply as a “medium”) has a particular range of frequencies or bandwidth, such as from 5 MHZ to 42 MHZ, that the signals travel at over the communication link. Additionally, the medium also refers to the physical path which the signal travels over from a transmitter to a receiver.
As these data-bearing signals propagate over the medium of the communication link, the signals experience distortion such that the signals being received at a corresponding receiver are altered from their transmitted form depending on noise levels, non-linearities, time delays and reflections that are all frequency and medium dependent upon the signals within the medium, for, example. Specifically, the amplitude and phase of the signals are distorted, which is referred to in the composite as medium dependent channel distortion (also referred to as “channel distortion”). If the channel distortion of the signal over a particular medium provides an acceptable signal to noise ratio, for example, the receiver demodulates the signal and extracts the data from the signal. Disadvantageously, if the channel distortion is too great or the signal to noise ratio is unacceptable, the receiver will demodulate the signals and potentially misinterpret the information or data carried therein.
Knowledge of the channel distortion of a particular communication medium (i.e., medium dependent channel distortion) provides an estimation of the quality of service of the particular communication medium. The quality of service for the particular communication medium limits the signaling that can be transmitted and received over the communication medium. For example, the quality of service for a particular medium effects what levels or grades of service, i.e. the modulation level and signaling rate, for signaling that can be supported by the medium. Thus, in order to determine what levels of service are possible over a particular medium, a quality of service is determined for the particular medium based upon channel distortion estimates.
In a communication network, it would be desirable to estimate the channel distortion for communication mediums between any number of nodes within the communication network in order to estimate the quality of service for various components of the network and to provide an indication of the health of the network. A communication network includes many communication mediums between many different nodes within the communication network. For example, a network hub communicates with many communication devices, i.e., subscriber devices, within the network, such that a communication medium is defined between each of the subscriber devices and the network hub. Each of these communication mediums may have a different level of medium-dependent channel distortion specific to that particular medium and resulting in potentially different quality of service estimations for one or more of the communication mediums. Thus, each of the communication mediums within the communication network may actually support different levels or grades of service, i.e. have a different quality of service estimation.
Additionally, many of these different communication mediums may share portions of the same physical communication path (also referred to as the communication link) between the respective subscriber device and the network hub. For example, in communication networks spanning a large geographical area, e.g. a hybrid fiber/coax (HFC) system, the physical communication path from one node, e.g. a subscriber device, in the network to another node, e.g. the network hub, may include physical portions that are shared by many communication mediums. Thus, simply estimating a quality of service for a particular communication medium within the communication network does not provide any information about which physical portion of the physical communication path utilized by the communication medium is, for example, limiting the quality of service supportable by the communication medium.
Dynamically allocated communication networks, in which a subscriber device is dynamically connected to a network routing device, i.e. a public switched telephone network (PSTN) switch hub, local area network (LAN), or wide area network (WAN), only allow the ability of the network to estimate a quality of service for the particular connection between the network routing device and the subscriber device during the current physical connection. This estimation of the quality of service is based upon the ability of the subscriber device to connect itself to the terminating device, i.e., the network routing device. Since the currently allocated physical connection path is for the current communication only, a subsequent physical connection from the network routing device to the same subscriber device may involve an entirely different physical connection path depending on the allocation of network resources, the availability of network resources, etc. Thus, any quality of service estimation for the communication medium involving the currently allocated physical path will only be valid for the duration of the connection, since the allocated physical path will likely be different in subsequent allocations by the network routing device. Thus, the prediction of what the next quality of service for the medium to that same subscriber will be ambiguous due to the dynamic switching element in the network that allocates the physical connection. Therefore, such quality of service estimations would not provide an indication of the health of the network over time, which may be used to indicate weak points within the network or to indicate a degradation of service over a localized section or path of network within the composite overall network.
In a relatively time-invariant (i.e. the transmitter and the receiver are relatively fixed in location with respect to one another) communications network that is non-dynamically allocated (i.e. the physical transmission paths are known and relatively static over time), such as a hybrid fiber/coax (HFC) system, estimation of medium dependent channel distortion for any one particular communication medium within the network is expensive and requires potentially obtrusive, dedicated equipment to be physically connected to both the transmitter and the receiver of the communications medium. For example, the network provider may connect different equipment, e.g. transmitters and receivers, each capable of transmitting and receiving signaling of differing levels of quality of service in order to determine if the medium will support such signaling. Alternatively, the network provider may physically connect an adaptive bandwidth and signaling rate scan receiver in the communication path that can switch between higher and lower modulation levels and signaling rates, such as the HP89441 VSA (Vector Signal Analyzer made by Hewlett Packard), along with an appropriate transmitter that can transmit signaling with the different modulation levels and signaling rates. Alternatively, a network analyzer, which is a two-port system, may be coupled to the transmit and receive end of the communications path to analyze the medium there between. Each of these devices requires physical connection at both ends of the medium, i.e. the transmitting end and the receiving end, and requires that any existing services be interrupted during the testing process. Thus, the use of such physically connected devices, especially in networks encompassing a large geographic area, at all nodes within a given network is prohibitively time consuming, expensive and results in the interruption of services (when present) to subscribers of the network. Furthermore, such equipment does not account for the fact that the tested physical communication path is likely shared with multiple communication mediums.
The present invention advantageously addresses the above and other needs.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings.